One year after the Air Force blasted it into orbit, an experimental robotic space drone continues to circle the Earth.
Its mission and payload, however, remain a mystery.
The X-37B Orbital Test Vehicle, which looks like a miniature unmanned version of the space shuttle, was launched last March from Cape Canaveral, Fla.
At the time, Air Force officials offered few details about the mission, saying that the space plane simply provided a way to test new technologies in space, such as satellite sensors and other components.
It was slated to land 270 days later, which would have been in November, on a 15,000-foot airstrip at Vandenberg Air Force Base, northwest of Santa Barbara, Calif. But the Air Force extended the mission and never announced an exact landing date.
Air Force Lt. Austin Fallin, a Vandenberg spokesman, confirmed Wednesday that the X-37B is still in orbit.
It is the second X-37B launched by the military. The first one was launched in April 2010 and landed 224 days later at Vandenberg.
Some industry analysts have theorized that because of its clandestine nature, the X-37B could be a precursor to an orbiting weapon, capable of dropping bombs or disabling foreign satellites as it circles the globe.
The Pentagon has repeatedly said the space plane is simply a "test bed" for other technologies.
Both X-37Bs were built in tight secrecy by Boeing Co.'s Space and Intelligence Systems unit in Huntington Beach, Calif. Engineering work was done at the company's facilities in Huntington Beach and Seal Beach. Other components were supplied by its satellite-making plant in El Segundo, Calif.
Explore further: Custom tailoring robotic exoskeletons that fit to perfection